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RF Electronics Chapter 8: Amplifiers: Stability, Noise and Gain Page 284 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. noise that will be obtained if the circuit is noiseless. If N a is the noise power at the amplifier output, and N i is the noise power at the input and G is the power gain of the amplifier. Often the noise is referred to the input. N e is the noise power of the amplifier output, referred to the input of the amplifier. The NF is thus: � � � �� � � �� � �� � � � � � � Eqn. 8.22 For an resistor of R , at an absolute temperature (K) of T 0 , has a noise voltage of: � � � 4 � Eqn. 8.23 Since P=V 2 /R, the thermal noise power (N 0 ) produced is independent of R: � � � Eqn. 8.24 The NF can thus also be written as: � � � �� � � � Eqn. 8.25 where T e is the equivalent noise temperature of the amplifier and is the additional noise temperature, referred to the input, that is caused by the amplifier and T 0 is the ambient temperature of the input of the amplifier. The noise performance of an amplifier is either; specified as a NF or as an equivalent noise temperature. Equation 8.25 allows the conversion from one to the other. Often amplifiers are used in cascade, with the output of one amplifier driving another. If the first amplifier has a noise figure of NF 1 and a gain of G 1 and for the amplifier that follows it is NF 2 , and G 2 and so on. Then for that system, the total NF and noise temperature can be shown to be: ����� � � � �� � �� � � � �� � �� � � � � � �� � �� � � � � � � �� Eqn. 8.26 ����� � � � � � � � � � � � � � � � � � � � � � � � �� Eqn. 8.27 These are known as Friis formulas for noise factor and noise temperature, after Harald T Friis [8]. They show that the NF of the first amplifier in a chain is the most critical. The NF of a Low Noise Block downconverter (LNB), such as shown in figure 11.4 [9], which are mounted at the focal points of satellite dishes and convert the satellite signal to signals around 1 GHz with a gain of more than 60 dB, is typically 0.6 to 0.9 dB. The NF of the LNB is the most critical parameter for these devices. It is difficult to design an amplifier, which has a very low NF and is stable. Examples The theory outlined above will now be applied to three different devices to illustrate the different ways that stability and noise information is obtained using AWR DE. Example 8.1: BGB707 MMIC The first example uses an Infineon BGB707L7ESD, Silicon Germanium Carbon Bipolar MMIC. The IC is designed as a low noise front-end amplifier for a wide range of applications like GPS, WLAN, LTE, WiMAX. The IC has a bandwidth of 50 MHz to 10 GHz, operates at 1.8V to 4V, has a minimum NF of 0.6 dB, has Electro Static Discharge (ESD) protection on all pins and is a relatively low cost device. The supply current and can be adjusted using a resistor from 2 mA to 10 mA, resulting in a different noise RF Electronics: Design and Simulation 284 www.cadence.com/go/awr

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